- Apr 4 Film serial "Perils of Pauline" shown for the first time in Los Angeles, California
- Apr 6 American Radio Relay League (organization for hams) founded
- Apr 8 US & Colombia sign a treaty concerning Panama Canal Zone
- Apr 9 "World, the Flesh & the Devil", 1st color film, shown in London
- Apr 9 Tampico incident - US ship crew arrested in Mexico
US Refuses to Recognize Huerta
Apr 9 US President Woodrow Wilson refuses to recognize Victoriano Huerta as President of Mexico on the ground that the dictator has not been elected by the people
Huerta Breaks with US
Apr 11 Mexican President Victoriano Huerta breaks off diplomatic relations with the US
- Apr 20 18th Boston Marathon won by Canadian James Duffy in 2:25:01.2
- Apr 20 Ludlow Massacre: Colorado Fuel and Iron (CF&I) security team and Colorado National Guard soldiers kill 21 workers, women and children during mine strike in Ludlow, Colorado
- Apr 20 US President W Wilson, having dispatched more naval ships to Mexico, asks a joint session of Congress to approve armed force if necessary; Congress approves
- Apr 21 US marines occupy Vera Cruz, a major Mexican port; they will stay for 6 months
- Apr 23 MLB Chicago Federals host the Kansas City Packers in the 1st game played at Weeghman Park (now Wrigley Field)
- Apr 24 A shipment of 35,000 rifles and 5 million rounds of ammunition are landed at Larne for the Ulster Volunteer Force (UVF, an Ulster loyalist paramilitary group in Northern Ireland
- Apr 25 US President Woodrow Wilson is persuaded by Argentina, Brazil, and Chile to accept mediation in the conflict with Mexico
- Apr 27 Honduras becomes a signatory to the Buenos Aires copyright treaty
- Apr 28 181 die in coal mine collapse at Eccles, West Virginia
Admirals
Aviators
Gangsters
Generals
Industrialists
Suffragists